When historians turn seaward the view include not only the coastline, but also the ocean which for a large part is not discernible by men directly. Thus ships, machines, gears, tools, instruments and skills have been critical for the attempts to understand the conception of the sea. Science was – and is- of critical significance as a way of knowing the sea, and the technologies used by scientist mediated crucial knowledge about the ocean. The contributers to the Symposium will through their cases-studies examine the importance of some of the tools and the methods used in the field studies on the ocean, in order to deepen the overall understanding of scientific practice and scientists at work.